Installing ESXi on a Drive with an Existing ESX or ESXi Installation or VMFS Datastore

ESXi 5.x uses the same installer for fresh installations and upgrades or migrations. If the installer finds an existing ESX/ESXi 4.x or ESXi 5.0 installation, it provides the option to upgrade or to do a fresh installation.

See vSphere Upgrade.

Depending on the disk layout of your system, the ESXi installer offers a choice between preserving or overwriting the VMFS datastore during installation.